Method and apparatus for drying and forming stereotype matrices



y 17, 1955 L. A. FRAZEE ETAL 2,708,318

METHOD AND APPARATUS FOR DRYING AND FORMING STEREOTYPE MATRICES Filed Oct. 21, 1952 3 Sheets-Sheet l LEONARD A. FRAZEEa DELMAR H. ELDER,

INVENTORS.

ATTORNEY- May 17, 1955 A. FRAZEE ETAL METHOD AND APPARATUS FOR DRYING AND FORMING STEREOTYPE MATRICES 3 Sheets-Sheet 2 Filed OGt. 2l,'l952 u I06 2| I04 :06

LEONARD A. FRAZEE a DELMAR H. ELDER,

INVENTORS.

ATTORNEY.

y 1955 L. A. FRAZEE ETAL 2,703,313

METHOD AND APPARATUS FOR DRYING AND FORMING STEREOTYPE MATRICES Filed 001;. 21, 1952 3 Sheets-Sheet 3 TI 7 IIIIIIIIIIIIIIIIIIIIIIII LEONARD A. FRAZEE a DELMAR H. ELDER, INVENTORS.

A 7' TORNE K United States Patent METHOD AND APPARATUS FOR DRYING AND FOTUAING STEREOTYPE MATRlCES Leonard A. Fraz-ee, Compton, and Delmar H. Elder, Seal Beach, Calif.

Application October 21, 1952, Serial No. 316,044

Claims. (Cl. 34-8) This invention relates to processes and devices for drying, shrinking and forming stereotype matrices in preparation for casting stereotype plate.

The well-known procedure for producing a cast semicylindrical stereotype plate for use in a rotary printing press is carried out first by setting up type in the usual rectangular chase and then obtaining a mold of the printed matter by pressing thereon a matrix in the form of a damp sheet of papier mach. The molded matrix must then be dried and formed accurately to cylindrical curvature so that it may be placed in a casting box for the casting of the final curved stereotype plate.

in the past it has been found exceedingly diflicult to produce a dried matrix accurately curved to the required semi-cylindrical configuration with a clear high-quality impression of the original type and without distortion. The difficulties arise largely from the fact-that a moist freshly-molded matrix is so soft and so easily damaged that it must be dried to at least an intermediate state of hardness before it can be safetly subjected to the forces necessary for forming it to accurate cylindrical configuration entirely free from buckles or other irregularities. In the initial drying period there is a persistent tendency for the matrix to form irregularities by warping and buckling out of shape. To remove these irregularities it is necessary to use relatively severe treatment in the subsequent forming operation but, unfortunately, such severe final treatment usually lessens the quality of the type impression. A further consideration is that the matrix shrinks as it dries and great care is required to avoid uneven shrinkage in the course of the preliminary drying treatment.

One cause of non-uniform shrinkage is non-uniform drying. Distortion from this cause is ditficult to avoid if heat is applied at a high rate to reduce the time necessary for drying and hardening and is especially so if the heat is applied to only one side of the matrix. Another cause of non-uniform shrinkage is the use of some means or the application of some force that unduly restricts the freedom of matrix for shrinking movement during the initial drying stage. Thus, any means used to apply pressure against the matrix or to hold the matrix in a positive manner during the initial drying period for the purpose of minimizing the formation of buckles during that period usually interferes with normal uniform shrinkage and therefor results in distortion in the final product.

All of the prevailing procedures for satisfactorily processing stereotype matrices involve two distinctly separate operations requiring two separate pieces of apparatus. The preliminary drying stage is carried out in some special heating device commonly known as a scorcher. The matrix is bent to curved configuration in the scorcher and at the same time is subjected to radiant heat. in some instances infra-red lamps are employed. The partially dried and partially hardened matrix is then placed in a suitable forming device wherein further heat is applied to dry and harden the matrix to the required final state.

In some prior practices, the second apparatus is a centrifugal drier having a rotary perforated cylindrical wall and involving the use of a suitable pressure blanket. The matrix is placed against the inner curved side of the perforated cylindrical wall with the impression side of the matrix inward, and the blanket is placed on the inner side of the matrix to press outward against the matrix when the perforated wall is rotated. Thus the blanket urged outward by centrifugal force serves as auxiliary means for placing the matrix under radial compression.

One disadvantage of this procedure is that the blanket completely covers the inner surface of the matrix to prevent adequate circulation of air over one side of the matrix. A more serious disadvantage of this procedure, however, is that the centrifugal pressure of the blanket reduces the quality of the impression in the finished product. To minimize this lowering of quality the preliminary drying and scorching prior to the centrifugal operation must be prolonged to harden the matrix more than usual but, unfortuntately, such prolonged initial drying results in stubborn buckles that can be removed only by excessive blanket pressure in the final drying operation.

In other instances in prevailing prior art procedures, the second operation consists of placing the partially dried matrix against the inner side of a fixed concave perforated plate and holding the matrix in place by a vacuum on the convex side of the plate while heat is radiated against the inner surface of the matrix. One drawback of this procedure is that the vacuum does not act uniformly on all of the fibers of the matrix and, moreover, the pressure differential created by the vacuum is reduced wherever air flows through the fibers of the matrix or around the edges of the matrix. A more serious drawback is that the inner side of the matrix tends to dry rapidly, both because heat is applied to the inner side and because vacuum draws moisture away from the inner side. The faster drying of the inner side increases the tendency for the matrix to buckle.

The side of the matrix that receives the impression of the type may be termed the impression side and the other side of the sheet may be termed the back side. The impressions of type create bulges in the matrix towards the back side of the sheet. On the other hand the blank spaces in the matrix, where no type impressions are made, bulge in the opposite direction towards the impression side of the sheet, there being corresponding recessed areas on the back of the sheet. These latter bulges on the impression side of the sheet where no type impressions occur and the corresponding recesses on the back side of the sheet may be relatively extensive in area, and it is customary, therefore, to reinforce extensive bulges against collapse by mounting adhesive backing strips of felt, or other suitable material, on the back side of the matrix in the recesses.

The prevalent prior art procedures not only inherently work against the quality of the finished product, as explained above but also are time consuming since each matrix must be handled twice for processing by the two different pieces of apparatus. It is also to be noted that capital investment in two pieces of apparatus is required and, moreover, room must be provided for two separate pieces of apparatus.

A further and important consideration is the lack of precise control in the prior procedures over the degree of shrinkage of the matrices. Shrinkage control has become especially important because the rising cost of paper has made it necessary in many instances to economize by reducing the size of the type and the columns of type. It is not feasible to change the size of the type in the rectangular case by changing or discarding the present typesetting equipment to save paper, but it is practical to shrink the stereotype matrices for the same purpose.

The present invention performs the necessary drying and forming operations in an inexpensive time-saving manner and results in a superior dried matrix that is accurately shrunk to predetermined dimensions without distortion. An important feature of the invention is that only a single piece of apparatus is employed instead of two pieces of apparatus and the one piece of apparatus automatically carries out the complete process in a single uninterrupted cycle of operation without attention by the operation. Time is saved not only because the single apparatus carries out a single cycle, but also because the process itselif is so effective that a relatively short time is sufiicient to produce the desired result. A further feature of the invention is that the apparatus may be used to produce a series of matrices in rapid succession with uniform quality, uniform shape and uniform dimensions throughout the series of matrices.

The invention accomplished these various desirable results by a new centrifugal treatment in which the moist, newly-formed matrix is held centrifugally against the inner side of a perforate cylindrical wall that rotates about its axis of curvature. No blanket or other means is used to press the matrix against the rotating cylinrical wall. Initially the cylindrical wall is accelerated to a low speed in a surrlciently graduated manner. to avoid damage by slippagealong the curved wall and to avoid displacement of the adhesive felt backing strips in the back recesses of the matrix. The curved perforate wall rotates in a zone heated by heating elements positioned outside the periphery of the curved Wall.

' The rate of rotation of the curved wall is sufficient to hold the matrix centrifugally against its inner surface 7 but is low enough to permit adequate freedom for the matrix to creep as required for uniform shrinkage.

Rotation is stepped up automatically after a preliminary time interval sufficient for the desired shrinkage and also sumcient for so hardening the matrix that it can withstand higher centrifugal force. rate of rotation in the second stage of the operating cycle with the consequent greater centrifugal force accelerates the extraction of the residual moisture, increases the rate of circulation of air to vaporize the moisture, increases the force tendin to hold the hardening matrix to the desired configuration, and causes the matrix to press against the curved perforate wall with sufiicient force to minimize further shrinkage of the matrix.

An important feature of the preferred practice of the invention is the manner in which acceleration of the cylindrically curved perforate wall is controlled for suitable gradual build-up to a first stage speed and for later build-up to the higher second stage. speed. The initial gradual acceleration to the first lower speed is achieved by the choice of a motor to operate a rotary structure of a given mass. The invention teaches. that a motor may be selected to provide relatively low starting torque and the first stage speed may be set relatively low so that the inertia of the rotary structure may be relied upon to retard initial acceleration to the required degree. Subsequent graduated acceleration to the higher speed of the second stage of the cycle, is provided by automatic shift of a special twospeed transmission for driving the rotary structure.

The invention with its features and advantages, may be further understood from the following detailed description in conjunction with the accompanying drawings.

In the drawings, which are to be regarded as merely illustrative,

Figure l is a vertical sectional view of the presently preferred embodiment of the invention;

Figure 2 is a view partly in plan and partly in section taken as indicated by the line 22 of Figure l;

The higher Figure 3 is a horizontal section taken as indicated by the broken line 3-4: of Figure 1;

Figure 4 is a diagrammatic view showing the general cross sectional configuration of a newly impressed matrix with an adhesive backing strip across a recess on the back side of the matrix; and

Figure 5 is a wiring diagram showing the preferred circuit arrangement of the device.

The presently preferred embodiment of the invention shown in the drawings includes a housing having a base or bottom' wall it}, an intermediate horizontal partition or platform 11, a semi-cylindrical front Wall 12, a semicylindrical back wall 13, two side walls 14, and a top wall 15. The top wall of the housing has a large circular opening 18 that is normally closed by a circular cover plate 19 having a handle 26. For access to the in tcrior of the housing at lower levels the side of the housing may be provided with one or more doors'or removable plates 21 (Figure 3). Preferably the housing is reinforced on the inside by a lower series of vertical metal rods 22 and a corresponding upper series of rods 23 which are held in place by suitable screws 24.

Mounted on top of the housing adjacent the rear wall 13 is an auxiliary horizontal plate to support a small,

cabinet 31 and switchbox 32 that is connected to the cabinet by a short horizontal tube 33. The plate 3! is anchored by suitable screws 34 and is mounted on suitable spacers 35 so that the circular cover plate 1 may be moved rearward under the plate 39 to expose the top housing opening 18 as shown in Figure 2.

The cabinet 31 has a forwardly facing inclined panel 39 on which is mounted the temperature adjustment knob 40 of a thermostat 41. The panel 39 also has a signal lamp 42 to indicate when the device is operating at its lower preliminary speed and a second signal lamp 43 to indicate when the apparatus is operating at its second higher speed. In addition the panel may be provided with a suitable clock 44 having a sweep second hand. The

clock 44 enables the operator to time the cycle of opera tion of the apparatus and is of assistance in making adjustments to change the cycle when desired. The switchbox 32 adjacent the cabinet has a start pushbutton 45 and a stop pushbutton 46.

Inside the housing is an upright rotor which is mounted on the platform 11 by a suitable thrust bearing 51 and is open at the top for access through the opening 18 in the housing. The structure of the rotor 56 includes a'base 52 having a hub portion 53 and includes an outer perforated cylindrical wall 55 and a similar inner concentric perforated wall 56 which may be made of smooth stainless steel or other suitable material. The outer cylindrical wall 55 is welded to the rotor .base' 52 and the inner cylindrical wall 56 is welded to a ring 57 that is anchored to the rotor base by suitable screws 53. Preferably a series of upwardly inclined fin ers 6i are provided at, the bottom of the inner wall 56 to retain a matrix in process of treatment. The curvature of the two cylindrical walls 55' and 56 corresponds to the curvature required in matrices for printing cylinders of two different diameters.

Preferably the rotor 50 is surrounded by a relatively thick cylindrical wall of heat insulating material 63 hav ing a metal liner 64. The insulating wall 63 together with the platform 11 and the top wall 15 of the housing forms a cylindrical drying chamber 65 which may be heated by any suitable means. The heating means shown in the drawing comprises six vertical 500' watt strip heaters 66 that are equally spaced around the inner circumference of the chamber, the upper ends of the stripheaters being interconnected by a ring 67 and the lower ends being interconnected by a second ring 63.

The rotor 50 is operatively connected with a vertical shaft 70 that is mounted in a suitable bearing '74 and is actuated by means of a sheave 75. The sheave is in turn actuated by a motor 76 through the medium of a suitable transmission or variable drive mechanism in such manner that the rotor is accelerated gradually from a standing start to the predetermined preliminary speed of rotation and is subsequently accelerated in a gradual manner to the higher speed of operation. Any suitable variable drive may be employed for this broad purpose.

The particular transmission arrangement that is shown in the drawing by way of example, includes three beveled sheave discs 78, 79, and 80 on an upright spindle 81 on one end of a horizontal lever 82.

The two sheave discs 78 and 79 cooperate to form a first variable split sheave designated A, and the two sheave discs 79 and 8t) cooperate to form a second variable split sheave designated B. A sheave 86 on the drive shaft 87 of the motor 76 is connected to the variable sheave A by a suitable V-belt 88 and in like manner the second variable sheave B is connected by a V-belt 99 with the previously mentioned sheave 75 on the upright shaft 70.

When the apparatus is idle or is operating at the preliminary or lower speed of operation, the variable sheave A is at an expanded efiective diameter and the second variable sheave B is at a contracted effective diameter. If, however, the lever 82 is rocked to shift the two variable sheaves A and B simultaneously towards the driven sheave 75 on the upright shaft 70, sheave A will respond by contracting in effective diameter and sheave B will respond correspondingly by increase in its effective diameter, the two variable sheaves functioning for this purpose in the well-known manner of transmissions of this character. it is apparent that the rate of acceleration of the rotor 59 from its preliminary low speed to its higher speed will depend upon the rate at which the lever 82 is shifted and the higher rate of speed will depend upon the extent to which the lever is wrought.

The lever 82 may be mounted in any suitable manner, may be adjustable with respect to its throw in any suitable manner, and may be actuated automatically in any suitable manner to carry out the purpose of the invention. In the construction shown in the drawings, the lever 82 is adjustably fulcrumed in the slot 93 of a fulcrum bracket 94 by a pair of adjustable screws 95, and the end of the lever is connected to the piston rod 96 of an actuator 97 that is powered by compression air.

The actuator 97, which is supported by a suitable bracket 93, is in the form of an air cylinder in which is mounted a piston (not shown), the piston being connected to the piston rod 96. Reciprocation of the piston is controlled by compressed air which may be supplied to opposite ends of the actuator by a pair of pipes 198 and 101.

The operation of the actuator 97 may be controlled, for example, by a suitable three-way valve 104, which valve may in turn be controlled electrically by a suitable solenoid ldS. The three-way valve 104 is mounted on a pair of support channels 196 and has an axially slidable valve member 107. As viewed in Figures 1 and 3, the valve member 197 is in its left position to admit compressed air to pipe 100 to hold the concealed piston in actuator 97 at its rightward position, the valve placing pipe 101 in communication with the atmosphere. If the valve member is shifted to its alternate right position, it will admit compressed air into pipe 1111 and place pipe 108 in communication with the atmosphere to cause the concealed piston to shift to its alternate leftward position. The valve member 107 is operatively connected to the operating core 111) of the solenoid 185 by an angular lever 112 in cooperation with a link 113 and the valve member is normally held in its leftward position by the tension of a suitable helical spring 114. The spring 114 is connected at one end to the solenoid core 110 and is connected at the other end to a fixed pin 115.

Compressed air is delivered to the three-way valve 184 through a supply line 118 that is controlled by a valve 119. Preferably the supply line is equipped with a suitable pressure gauge 121'). The rate at which the actuator 97 functions in response to shift of the valve member 1157, may be regulated in various ways. Preferably the rate is varied by varying the pressure of the air supply, but the rate may also be varied by adjustment of the valve 119 to vary the rate of air supply.

The preferred electrical arrangement for the apparatus may be understood by reference to the wiring diagram in Figure 5. A master knife switch is connected by three wires 131, 132, and 133 to a well-known type of magnetic starter switch designated by the dotted rectangle 134 and the starter switch in turn is connected to the motor 76 by three wires 135, 136, and 137. The six strip heaters 66 are energized by a circuit that includes the thermostat 41 and a pair of wires 138 and 139 that are connected to wires 131 and 133 between the knife switch and the starter switch. Thus closing the knife switch 131'; permits the apparatus to heat up to operating temperature prior to starting the motor 76. The clock 44 which is of the self-starter type is energized by the secondary of a step down transformer 140, the primary of the transformer being connected in parallel with the motor 75 by a pair of wires so that the clock will start and stop in synchronism with the motor.

The wiring diagram includes two time-delay relays of a well-known type that includes a bellows and is retarded in its action by a dashpot arrangement. One time delay relay 146, which may be termed the low speed relay, has a pair of normally closed contacts 147 and a pair of normally open contacts 148. The normally closed contacts 147 remain closed throughout the time delay period and then at the end of the period the contacts 147 open and the normally open contacts 148 simultaneously close. The second relay 151), which may be termed the high-speed relay, has a pair of normally closed contacts 151 which open at the end of a predetermined time delay period.

The motor control includes the previously mentioned push-button start switch 45 and the push-button stop switch 46 WhlCh are connected in series with the magnet M of the starter switch 134, with start push button 45 being connected in the usual manner in parallel with a pair of contacts 155 of the main starter switch 134. The circuit that magnetically closes the main starter switch .134 and normally holds the starter switch closed magnetically includes a wire 156 that connects the stop button 46 in series with the normally closed contacts 151 of the high-speed relay 1511-. T his circuit is completed by a wire 156 connected to the two norm-ally closed contacts 151, a second wire 157 and a third wire 158 that is connected to 3 the wire 137 of the motor circuit.

The low-speed relay 146 is connected in parallel with the motor 76 by a wire 156 that is connected to the motor lead 135 and by the previously mentioned wire 158 that is connected to the motor lead 137. When the low-speed relay 146 is initially energized, the low-speed lamp 42 is energized by the following circuit: Wire 16%, wire 161, the normally closed contacts 147 of the low-speed relay, wire tea, lamp 42, wire 143, and the previously mentioned wires 15! and 158.

At the end of the time delay period of the low-speed relay 1%, the normally open contacts 148 close to energize the high-speed relay 15%; through the following circuit; wire 16%, wire 161, contacts 148, a wire 167, highspeed relay 15%, and the previously mentioned wire 156. It will be noted that both the high-speed lamp 43 and the solenoid 1155 are connected in parallel with the highspeed relay 1511 by a wire 16S and by the previously mentioned wire 157.

The operation of the described apparatus may be readily understood from the foregoing description. Before starting production, the knife switch 130 is closed to energize the strip heaters 66 to bring the apparatus up to normal operating temperature.

The various adjustments with respect to temperature, the speed of rotation in the two stages of the operating cycle, and the duration of the two stages, may be understood by considering a specific example. In this example, the damp matrix that is initially impressed by the set type is sixteen and a half inches wide and is to be shrunk by one and one-sixteenth inch to a final width or" fifteen and seven-sixteenths inches. With this degree of shrinkage in mind, the starting matrix has a moisture content predetermined at eighteen per cent and the thermostat 41 is set to hold the temperature in the chamber 65 at 300 degrees.

When the matrix receives the pressure impression from the set type, it has the cross sectional configuration of the fragment of a matrix 170 shown in Pig. 4. The impression side of the matrix has small recesses or sharp indentations 171 which are the impressions of the set type and has various relatively large areas where no printed matter occurs. Thus in Figure 4 the relatively large area indicated by the bracket 174 represents a blank space on the printed page. ltwill be noted that with respect to the impression side of the matrix this area is a plateau which is formed by an extensive recess of the same area on the back of the matrix, which back recess is designated by the bracket 175. It is highly important that the plateau 1'74 and the corresponding back recess 75 be preserved completely throughout the processing of the matrix so that in the final casting of the type plate the plateau 174 will form a corresponding peripheral.

recess in the curved type plate with the bottom surface of the peripheral recess uniformly spaced inward from the type of the cast plate. Otherwise the cast plate will make contact with the print paper to cause ink smears in v the areas that properly should remain blank.

in accord with the usual practice, the various plateaus 174 of the newly int-pressed matrix are reinforced against collapse by the application of suitable backing strips or spacer strips on the back side of the matrix. Thus Figure 4 shows a backing strip 178 extending across the major portion of the back recess 1'75. The material for the backing strip $73 is usually a felt tape having a pressure sensitive adhesive on one face. The operator merely tears oil short *ieces of the backin tape and resses the r b 4 short pieces into place across various recesses in the back of the matrix in accord with his judgment.

In this particular example in which the initial water content of the matrix is eighteen per cent, or in the range of eighteen to twenty per cent, and in which the temperature setting of the thermostat is 300 degrees, a product of excellent quality is obtained by adjusting the low-speed relay 146 for a time delay period of ten seconds and adjusting the high-speed relay id) for a time delay period of one minute and twenty-five seconds. Since the newly impressed matrix is soft and highly vulnerable to damage, it must be subjected to only very mild treatment until it reaches at least an intermediate stage of hardness and even then care must be taken to avoid rough handling and excessive stresses until it reaches a relatively advanced stage of hardness. The various backing strips 178 are also highly vulnerable since they may be displaced only too easily. in fact the degree to which a moist matrix can be accelerated for centrifugal drying operation is severely limited by the tendency of the backing strips 178 to become displaced by slippage in response to such acceleration.

The matrix to bc dried, shrunk, formed and hardened, is placed either inside the outer perforate cylindrical Wall 55 or inside the inner perforate cylindrical wall 56, according to which curvature is required in the final prodnot. in eitner case the matrix is placed in position to stand on its edge against the inner face of the cylindrical perforate wall with the impression side of the matrix facing inward from the perforate wall and with the back side of the matrix lying against the wall. Thus the various hacking strips 178 will lie against the cylindrical perforate wall to support the various plateaus 174 of the matrix against collapse outwardly by centrifugal pressure. An important feature of the present apparatus is that there is room for two matrices for simultaneous processing against the outer perforate cylindrical wall 55, this outer cylindrical wall having the radius of curvature required for newspaper printing. if the-smaller curvature is required in the finished product, the matrix is dropped into the inner cylindrical Wall 56 and is held in place by the fingers 66.

After a matrix or a set of matrices is installed inside the rotor 50 the operator replaces the cover plate 19 and presses the starting button 46. In the present example, he apparatus is adjusted for an initial speed or first stage operation at 400 R. P. M. and is adjusted for operation in the second stage at 1800 R. P. M. It will be readily understood that these two speeds are determined by the adjustment of the two screws as may be understood by referring to Figure 3. At the low speed position of the lever 82, when the piston rod 96 is in the rightward position shown in Figure 3, the lever 82 fulcrums against the righthand screw Q5. Thus the normal lowspeed position of the lever may be varied by adjustment of the righthand screw. The first stage speed of rotation may be increased by screwing the screw outward to shift the lever 32 towards the driven sheave 75 and, conversely, the first stage speed may be set at a lower R. P. M. by tightening the lefthand screw 95. In the second stage of the operating cycle when the piston rod 96 is in its leftward position the lever 82 fulcrurns against the leftward screw 95. The effect of tightening the leftward screw 5v is to increase the second stage speed of the apparatus and, conversely, the effect of loosening the leftward screw 95 is to decrease the second stage speed.

The mass and weight distribution of the rotor 50 and the torque of the motor 76 are such that the combination of inertia of the rotating mass of the rotor and the torque produced by the motor, results in a sufficiently gradual acceleration to the first stage speed of 460 R. P. M. that there is no danger of damage to the initially soft matrices in the rotor and no possibility of the various backing strips 178 being displaced from their proper positions. This inital acceleration may extend over the major portion of the ten'second delay period for which the lowspeed relay 146 is set. During this initial period of operation of the motor 76 the low-speed lamp 42 is energized. At the end of the ten-second delay period,

the normally closed contacts 147 of the low speed relay 146 open to de-energize the low-speed lamp 42 and at the same time the normally open contacts 143 of the relay close to energize the high-speed relay 156 in parallel with the low-speed relay.

The closing of the normally open contacts 148 causes the high-speed lamp 43 to light up and at the same time energizes the solenoid to operate the three-way valve 194. The operation of the three-Way valve 194 reverses the air supply to the actuator 97 and thereby causes the piston rod 96 to move gradually to its alternate leftward position with consequent swinging of the lever 82 counterclockwise from the position shown in Figure 3. This rocking movement of the lever 32 causes split sheave A to contract in effective diameter and causes split sheave B to expand in effective diameter as heretofore explained, thereby increasing the ratio between the speed of the driven sheave 75 and the speed of the drive'sheave 86. This second acceleration of the rotor 58 is retarded to the desired degree by the manner in which compressed air is delivered to the actuator 97 and may be controlled, for example, by adjustment of the valve 119. At the end of the time delay period of the high speed relay 159, the normally closed contacts 147 open and thereby release the main starter switch 13 to de-energize the motor 76.

When the low-speed relay is adjusted for a ten-second delay period, the acceleration from the first stage speed to the second higher stage speed follows closely on the accleration from a standing start to the initial first stage speed. Que way of regarding the operation therefore,

is to consider the apparatus as operating with prolonged acceleration from a standing start to a maximum speed of operation which acceleration is sufiiciently prolonged to permit the centrifugal drying effect in the combination with the drying effect of the strip heaters 66 to progressively harden the matrix in process at a suf icient rate to enable the matrix to withstand the acceleration stresses and the increasing centrifugal stresses without damage. If the low speed timer is adjusted for a ten second delay period the total acceleration period, including acceleration by the automatically varied transmission, may be approximately thirty seconds, for example, in which period of time the matrix hardens sufficiently to withstand the maximum speed of rotation.

During the initial first-stage treatment of the matrix there is suflicient centrifugal pressure engendered to hold the matrix in close conformation with the curvature of the adjacent perforated cylindrical wall and to cause moisture in the matrix to migrate centrifugally outward towards the side of the matrix that is exposed to the strip heaters 66. It is important to note that in this manner a certain uniformity in drying action is achieved since the drying effect of the centrifugal action is primarily effective on the inner side of the matrix and the drying effect of the strip heaters is primarily effective on the outer side of the matrix. It is also important to note that the inner side of the matrix is the impression side, which side is not subject to pressure contact and is not exposed to the scorching and warping effect of direct heat radiation.

It is to be clearly understood, that during the initial stage of operation or during the major portion of the initial period of protracted acceleration during which the matrix shrinks at a substantial rate, the centrifugal force engendered is not suflicient to interfere with the creepage of the matrix relative to the adjacent perforate wall. As the matrix hardens to a smooth finish by reason of its contact with the smooth surface of the perforated wall, the co-efficient of friction between the matrix and the perforated wall naturally decreases so that increasing speed is permissible Without interfering with the shrinking action. By the time the apparatus reaches its maximum speed, the shrinkage of the matrix is substantially completed. The centrifugal forces engendered at the maximum speed are sufficient to overcome any tendency of the matrix to buckle or otherwise depart from the desired cylindrical configuration and consequently the finished product in a hard matrix of accurate curvature ree from any distortion whatsoever. There is some reason to believe that the first stage speed should not exceed 500 R. P. M. to avoid interference with uniform shrinkage but that the second stage speed should be substantially greater than 500 R. P. M. to terminate the shrinkage by immobilizing the matrix relative to the cylindrical wall and to prevent buckling of the matrix as it reaches final hardness.

When the mode of operation of the apparatus is understood, the various adjustments necessary for handling matrices of various initial moisture content and for producing various degrees of shrinkage are readily ascertained by an operator of the skill expected in this art. In general the greater the shrinkage that is desired, the greater the initial moisture content and since the vulnerability of the matrix to damage increases with the initial moisture content, the lower the first-stage speed of operation and the more prolonged the first-stage speed. The lower speed of operation during the first stage of the cycle is desirable to avoid damage to the relatively moist matrix either by acceleration or by centrifugal force and the prolongation of the first stage is required both for the sake of permitting the desired high degree of shrinkage and for the sake of permitting the matrix to become sufiiciently hard to withstand the effect of acceleration to the maximum speed of rotation. Thus to process a matrix having an initial moisture content of 25% to obtain a relatively high degree of shrinkage,

the low-speed relay may be set for a delay period of at least 45 seconds and the apparatus may be set for initial low-speed operation at, say, 250 R. P. M. The second stage speed may be increased from 1800 R. P. M. to 2400 R. P. M. and in some instances it will be found advisable to raise the temperature setting of the thermostat.

On the other hand, when relatively little shrinkage is required, the initial moisture content of the matrix can be as low as 13% and the time delay period of the lowspeed relay may be reduced to cause relatively rapid acceleration to the maximum speed.

The exceptionally high quality of the finished product is obtained by avoiding excessive stresses in the material of the matrix during the initial drying period, and by both uniformly drying the matrix and uniformly stressing the matrix with centrifugal force from the very start of the process. As heretofore pointed out, the use of a vacuum to hold a matrix against a perforate forming wall does not result in uniform stressing of the matrix and neither does a centrifugally actuated blanket stress all the matrix fibres equally.

Our description in specific detail of'the presently preferred embodiment of the invention will suggest to those skilled in the art various changes, substitutions and other departures from our disclosure that properly lie within the spirit and scope of the appended claims.

Having described our invention, we claim:

l. A method of shrinking a stereotype matrix to a predetermined degree and at the same time forming the matrix to a predetermined cylindrical curvature, including the steps of: placing the matrix moistened with predetermined water content against the inner face of a smooth perforate wall of the predetermined cylindrical curvature; rotating said wall about its axis of curvature for a preliminary time period at a speed high enough under 1000 R. P. M. to drive the moisture in the matrix toward said wall centrifugally but low enough to permit the matrix to creep relative to the wall for uniform shrinkage of the matrix; simultaneously heating the region of the rotating wall to vaporize the moisture that is centrifugally driven radially outward of the matrix; and after a time delay for shrinkage of the matrix, raising the speed of rotation of the wall to a maximum speed sufiicient to immobilize the matrix against the wall and maintaining said higher speed of rotation and continuing to heat the region of the rotating wall until the matrix hardens to permanent form.

2. A method as set forth in claim 1 in which the matrix is provided with adhering backing strips and in which the wall is brought to said preliminary speed of rotation and is subsequently brought to the higher speed of rotation with sufficiently gradual acceleration to avoid shift of said hacking strips relative to the matrix.

3. A method as set forth in claim 1 in which said preliminary speed is substantially less than 500 R. P. M. and said hi her subsequent speed is substantially greater than 500 R. P. M.

4. A method as set forth in claim 1 in which the step of heating the region of the rotating wall is accomplished by radiating heat radially inward towards the wall to vaporize the moisture that is driven radially outward by centrifugal force.

5. in an apparatus of the character described for processing a moist stereotype matrix having adhering backing strips at the non-printing areas thereof, the combination of: a rotary perforate cylindrically curved wall for support of a matrix against its inner curved surface under pressure created by centrifugal force acting solely on the matrix; a series of heating elements spaced radially outward from said wall to heat said matrix; a prime mover to operate at substantially a given speed; means including a transmission operatively connected to said, prime mover and to said perforate wall to rotate saidwall about its axis of curvature, said transmission being shiftable progressively to progressively increase the speed of rotation of the curved wall from a relatively low speed of rotation relative to the prime mover to a relatively high speed of rotation relative to the prime mover; means to energize said prime mover with said transmission at its low speed adjustment to bring, said rotary wall up to said low speed, the mass of the moving parts and the power of the prime mover being such as to cause acceleration of the rotary wall at a sufficiently graduated rate to avoid displacement of said adhering backing strips; means to shift said transmission to its high speed adjustment; a timer responsive to said energization means to operate said shifting means at the end of a predetermined time period; and a second timer to de-energize said prime mover at the end of a second predetermined time p-.riod.

6. in an apparatus of the cnaracter described for drying a moist stereotype matrix, means to actuate a rotary perforate wall, said actuating means comprising: a first actuating means to operate at a substantialiy constant speed; means including a transmission operatively connecting said first actuating means and said cylindrical wall to rotate the cylindrical wall on its axis of curvature, said transmission being shiftable progressively to progressively increase the speed of rotation of the cylindrical wall from a lower speed to a higher speed relative to the speed of said first actuator; a second actuating means to shift said transmisison gradually from its low speed adjustment t its higher speed adjustment; and

' means to energize said first actuating means and said second actuating means in succession with a predetermined intervening time period to permit said rotary cylindrical wall to accelerate to said low speed and then subsequently to accelerate gradually to said higher speed.

7. An apparatus as set forth in claim 6 which includes means to tie-energize said first actuating means automatically at the end of a predetermined time period after energization of said second actuating means.

8. in an apparatus of the character described for drying a moist stereotype matrix, means to actuate a rotary perforate Wall, said actuating means comprising: a first actuating means to operate at a substantially constant speed; a pair of coaxial variable diameter sheaves interconnected to' rotate together and to vary in diameter inversely relative to each other, said two sheaves being shiftable bodily between a normal low speed position with one of said sheaves at expanded diameter and a high speed position with said one sheave at contracted diameter; means including a belt operatively connecting said first actuating means to said one sheave; means including a belt operatively connecting the other of said sheaves to said rotary cylindrical wall; a second actuator to shift said pair of sheaves gradually from said normal lo v speed position to said high speed position with consequent tensioning of said first belt to contract said one sheave and to expand said other sheave; means to energize said first actuating means with said pair of sheaves at said normal low speed position thereby to accelerate said cylindrical wall to a predetermined low speed; means including timer means to energize said second actuating means with predetermined delay after energization of said first actuating means; and means to de-energize said first actuating means at the end of a predetermined period of operation.

9. In an apparatus of the character described for drying a moist stereotype matrix, means to acuate a rotary perforate wall, said actuating means comprising: a first actuating means to operate at a substantially constant speed; a pair of coaxial variable diameter sheaves intera belt operatively connecting the other of said sheaves with said rotary cylindrical wall; an air motor to shift said pair of sheaves gradually from said normal low speed position to said high speed position with consequent tensioning of said first belt to contract said one sheave and to expand said other sheave; a control valve for said motor having a normal low speed position and a high speed position; a solenoid to shift said valve from its low speed position to its high speed position thereby to'cause said air motor to shift said pair of sheaves from their low speed position to their high speed position; and switch means to energize said first actuating means and said solenoid in predetermined time sequence.

10. An apparatus as set forth in claim 9 which includes means to vary the rate of airflow into said air 12. In an apparatus of the character described for dr ing a moist stereotype matrix, means to actuate a rotary perforate wall, said actuating means comprising: a motor; a variable drive transmission operatively connecting said motor to said perforated cylinder, said transmission being shiftable from a relatively low speed ratio to a relatively high speed ratio, fluid pressure actuated means to shift said transmission from its low speed adjustment to its high speed adjustment; a valve to control said fluid actuated means; a solenoid to control said valve; switch means to energize said motor with said transmission at its low speed adjustment; and a time delay switch to energize said solenoid at the end of a predetermined period operation of the motor thereby to actuate said valve for causing said fluid pressure actuated means to shift said transmission to its high speed adjustment.

13. An apparatus of the character described for drying a moist stereotype matrix, comprising: a rotary, perforate, cylindrical, curved wall for support of a matrix against its inner curved surface under pressure created by centrifugal force acting solely on the matrix; a first actuating means for rotatably driving said curved wall about its axis of curvature at a substantially constant relatively low rate of speed; a second actuating means for rotatably driving said curved wall at a relatively high speed; means to energize said first actuating means and said second actuating means in succession with a predetermined intervening time period to permit said rotary cylindrical wall to accelerate to said low speed and then subsequently to accelerate gradually to said higher speed; and means for de-energizing said second actuating means t the end of a second intervening predetermined time period.

14. An apparatus of the character described for drying a moist stereotype matrix, comprising: a smooth perfo-' rate wall of predetermined cylindrical curvature; means for rotatably mounting said wall for rotation about its axis of curvature; a first means for rotatably driving said wall at a relatively low speed high enough to drive the moisture in the matrix towards said wall ceutrifugally but low enough to peimit the matrix to creep relative to the wall for uniform shrinkage of the matrix; means mounted contiguous to said wall for heating the same to vaporize the moisture driven'radially outward of the matrix; means, including a time-controlled means, for de-energizing said first means after a predetermined time period; second means rendered operative by said last named means at the termination of said predetermined time period for rotatably driving said wall at a relative high speed of rotation to immobilize the matrix against the wall; and means for tie-energizing said second means after a predetermined interval of time suificient to permit the matrix to dry and harden to a permanent form of a curvature determined by said cylindrically curved- Wall.

15. In an apparatus of the, character described for processing a moist stereotype matrix having adheringbacking strips at the non-printing areas thereof, the combination of: a rotary, perforate, eylindrically curved wall for support of a matrix against its inner curved surface under pressure created by centrifugal force acting solely on the matrix; a series of heat elements spaced radially from said wall to heat said matrix; means for rotatahly driving said curved Wall about its axis of curvature, said means operable to rotatably drive said wall at a relatively low speed of rotation, the mass of the moving parts and the power of the driving means being such as to cause acceleration of the rotary Wall at a sufliciently graduated rate to avoid displacement of said adhering backing strips; means to energize said driving means to bring said rotary wall up to said low speed; means for rotatably driving said curved wall at a relatively high speed of rotation; a timer for rendering inoperative said relatively low speed driving means at the end of a predetermined time period i4 and including means for energizing said high speed driving means; and a second timer to de-energize said high speed driving means at the end of a second predetermined time period.

References Cited in the file of this patent UNITED STATES PATENTS 1,799,649 Schenck Apr. 7, 1931 1,931,749 Bigsby Oct. 24, 1933 2,120,471 Peters et a1. June 14, 1938 2,188,528 Clark Jan. 30, 1940 2,350,934 Schutte June 6, 1944 2,618,073 Finzer Nov. 18, 1952 2,679,078 Clark May 25, 1954 FOREIGN PATENTS 605,579 Germany Nov. 20, 1934 

